Research In Motion meant nothing for most people while the Blackberry brand was strong and instantly recognizable. 37Signals was also renamed after the much stronger brand of their core product. Apple and iPhone are both just as powerful.

Companies like Apple, Nike, Mercedes, Coca-Cola will never completely change the name (maybe some variations here and there, without touching the core name) simply because the brand is so recognizable. It would be throwing money and image down the drain and it would just cause confusion.